To date, the greatest volume of research on the biodegradability of eco-plastics is regarding bioplastics, and specifically PLA, the most common, starch-based kind. Here's what we know:

PLA is, in fact, biodegradable, but it's not easily biodegradable [source: Teschler]. We don't know what the actual time frame is for landfill conditions. The stuff should break down after it's dumped, but there's no definitive evidence on whether that'll happen quickly or just eventually. As for degrading in compost bins, some research says it'll take anywhere from three months to one year; others have found that it won't happen at all in home compost settings -- that only commercial setups will be able to break the stuff down [sources: Worldcentric, Teschler].

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We do know that until it breaks down, it'll be taking up as much space as the petroleum-based plastic. Bioplastic containers typically contain at least as much material as traditional plastic containers.

Besides solid-waste volume and the tendency to biodegrade, another big issue surrounding eco-plastics is energy consumption. Does manufacturing the "green" plastic containers use less energy than manufacturing petroleum-based containers? The jury is still out on that one. Some say it uses about the same amount, because shaping starch-based material into cup form doesn't take any less effort than shaping fossil-fuel-based material into cup form [source: Teschler]. One point to remember here, though, is that companies in the eco-plastic business are more likely to adopt alternative- or low-energy processes, since they're aiming for the "green" market. The bioplastics company Ingeo, for instance, has instituted new manufacturing processes that reduce its greenhouse gas emissions by 60 percent and its overall energy needs by 30 percent [source: GD]. According to the company, creating Ingeo bioplastic now emits 77 percent less CO2 than creating typical petroleum-based plastic.

One definitive environmental downside to bioplastics is land use. Growing all that corn or sugarcane or beetroot takes a lot of farm land that could otherwise be used to grow crops for food or ethanol. On the other hand, if we've got to have our plastics, it could be worth the sacrifice: When the food company ConAgra switched from petroleum-based plastic to PLA plastic for the shrink wraps on some of its products, including Parkay and Fleishmann's margarine, it estimates it cut in CO2 footprint by half a million pounds [source: GD]. Imagine if they started making the tubs from bioplastics, too.

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